Conventionally, a heat pump type heating apparatus of this type has generated hot water to be used for heating, by using, as a heat pump unit, a refrigeration circuit through which a refrigerant circulates. For example, a heat pump type heating apparatus disclosed in Patent Literature 1 includes: a heating unit that causes a heating medium to circulate into a heating terminal; a first stage side heat pump unit in which a refrigerant circulates through a first compressor, a first heat exchanger, a cascade heat exchanger, a first expansion valve, and an evaporator, in order, and exchanges, at the first heat exchanger, heat with the heating medium of the heating unit; and a second heat pump unit, in which a refrigerant circulates through a second compressor, a second heat exchanger, a second expansion valve, and the cascade heat exchanger, in order, and exchanges, at the second heat exchanger, heat with the heating medium of the heating unit.
A conventional heat pump type heating apparatus including first and second stage side heat pump units, as disclosed in Patent Literature 1, performs control of shifts among a single-stage operation in which a first stage (low stage side) compressor is operated and a second stage (high stage side) compressor is stopped, a dual-stage operation in which both the first compressor and the second compressor are operated, and a standby operation in which both the first compressor and the second compressor are stopped, on the basis of the temperature (a return heating-medium temperature) of a return heating medium flowed out of a heating terminal.
For example, when, in the single-stage operation, the current temperature of a return heating medium falls below a prescribed low temperature threshold, the operation is shifted to the dual-stage operation by additionally starting the second compressor. When, in the dual-stage operation, the current temperature of the return heating medium exceeds a prescribed high temperature threshold, the operation is shifted to the single-stage operation by stopping the second compressor. When, in the single-stage operation, the current temperature of the return heating medium again exceeds the prescribed high temperature threshold, the operation is shifted to the standby operation by additionally stopping the first compressor.
In this way, the conventional heat pump type heating apparatus has determined the insufficient heating performance of the heating terminal on the basis of the return temperature of the heating medium flowed out of the heating terminal, shifted the operation among the single-stage operation, the dual-stage operation, and the standby operation, and thereby, tried to achieve an efficient heating operation.